1. Technical Field of the Invention
The present invention relates to methods for sealing electrochromic devices and devices manufactured thereby. Specifically, these methods are well-suited for manufacturing electrochromic devices--including electrochemichromic devices--in which electrochromic media--including electrochemichromic solutions--is placed in the cell cavity created therein. These devices are capable of varying the amount of light transmitted therethrough when an applied potential is introduced thereto. In that regard, the present invention relates to methods for sealing such devices which engage a sealing means to enclose the periphery of the cell cavity which has been created from the combination of at least two transparent substrates with the sealing means positioned therebetween. In this manner, the media may be contained within the cell cavity. Such sealing means hermetically seal the media within the device so that it is prevented from escaping therefrom and is also shielded from the external environment.
2. Brief Description of the Prior Art
Devices employing electrochromic and electrochemichromic technology are known [see, e.g. N.R. Lynam, "Electrochromic Automotive Day/Night Mirrors", SAE Technical Paper Series, 870636 (1987) ("SAE Paper I"), N.R. Lynam, "Smart Windows for Automobiles", SAE Technical Paper Series, 900419 (1990) ("SAE Paper II") and N.R. Lynam and A. Agrawal, "Automotive Applications of Chromogenic Materials", Large Area Chromogenics: Materials & Devices for Transmittance Control, C.M. Lampert and C.G. Granquist, eds., Optical Engineering Press, Washington (1990)]. Specifically, in connection with the manufacture of electrochromic devices and the technology engaged in the same, see U.S. Pat. Nos. 3,521,941 (Deb) and 4,712,879 (Lynam), and C.M. Lampert, Solar Energy Materials, 11, 1 (1984). And, in connection with the manufacture of electrochemichromic devices and the technology employed for the same, see U.S. Pat. Nos. 3,280,701 (Donnelly); 3,282,157 (Jones); 3,282,158 (Jones); 3,282,160 (Jones); 3,283,656 (Jones); 3,451,741 (Manos); 3,453,038 (Kissa); 3,806,229 (Schoot) and 4,902,108 (Byker). Despite this knowledge, those of ordinary skill in the art have been faced with the problem of efficiently incorporating these technologies into the manufacture of commercial devices.
Briefly, in the manufacture of these devices, glass substrates are typically positioned in spaced-apart relationship to one another and are separated by a seal which is placed on the periphery thereof which, when viewed in combination, creates a cavity in which the media is placed. The seal not only provides a means of ensuring the integrity of the cell which prevents media from escaping therefrom, but also assists to prevent the electrodes or conductive coatings (located on the interior faces of each of the glass substrates) from contacting one another and thus decreases the chance of short-circuiting the system.
The seals employed heretofore have often been constructed from an epoxy resin with a hardening agent combined therewith. Spacer beads of substantially uniform dimension--e.g., glass beads having a diameter of about 150 .mu.m--have also often been positioned on the interior face of a first substrate to assist in keeping the substrates distanced in their spaced-apart relationship when positioned together.
The epoxy resins have typically been applied to these substrates with a silk-screening instrument so that a thickness of about that of the spacer beads is obtained. After pre-curing the epoxy resin so that it reaches a semi-hardened state, a second substrate is positioned over the first substrate, and the two substrates subsequently pressed together so that the epoxy resin forms a continuous seal about the periphery thereof. The substrates are then held together under pressure, and the assembly generally fired in an oven, to fully cure the epoxy seal.
The epoxy resins, which are thermosetting materials, are provided initially, by their very nature, in an uncured state. Thus, because these materials have insufficient physical strength to secure the two substrates together in their uncured form, the seal needs to be cured prior to dispensing media into the interpane cell cavity. This is particularly true for media that comprises electrochemically active compounds dissolved in organic solvents since organic solvents may hinder the curing of the epoxy resins into seals. And, the electrochemically active compounds may be degraded when contacted with the components commonly used in the formation of seals from thermosetting materials. For these reasons, it has been the convention to fully establish and cure the seal prior to--rather than concurrently with--filling the interpane cell cavity so established with electrochromic media.
To that end, in one conventional method for filling such a device, the media is introduced into the interpane cavity by a small gap--e.g., less than 1 mm .times.1 mm.times.150 .mu.m--which is allowed to remain in the seal of the device during assembly. Typically, this gap is located at a corner thereof and acts as a "fill hole". Due to the fact that typically there is only one hole, which is itself small, filling the cell cavity is often difficult because of the back pressure created from within.
In another conventional method, known as the vacuum backfill technique, the empty device is placed in a vacuum chamber along with a container--e.g., a dish or small cup--of the media intended to be placed in the cell cavity through the fill hole. This chamber is generally evacuated under a vacuum of about 1 mm Hg or lower and the fill hole is then lowered into the container, just beneath the surface of the media. The chamber is then vented to atmospheric pressure--i.e., using nitrogen or some other inert gas--and the media forced into the cell cavity of the device until it is filled. Once filled, the fill hole is plugged and itself sealed in a secondary operation. In practice, such fill holes have proven to be weak points in the overall integrity of the sealed device. And, this technique is somewhat limited by the size and shape of the device to be filled.
Generally, when filled by any of these methods, a cosmetically unacceptable gaseous bubble may form and thereafter remain within the cell cavity of the device. While a small bubble of about 1 mm diameter will often dissolve over time, a larger bubble will not typically completely disappear. The choice of media solvent will often affect the formation and size of the bubble after vacuum backfilling a given device. In that regard, it is difficult to fill the device at room temperature with a highly viscous media--i.e., a gel or semi-solid media. Thus, in order to render the media less viscous, elevated filling temperatures are resorted to in an effort to render the media more fluid. This may cause degradation of the constituents of the media over prolonged periods of time as well as encourage the residual bubble to become even larger. The undesirability of these methods therefore becomes even more resounding.
U.S. Pat. No. 4,761,061 (Nishiyama) describes a further method of manufacturing these devices. There, two or more inner banks are constructed from pre-cured sealing materials and are thereafter placed at the periphery of the substrate of such a device. The inner banks are positioned between an uncured outer bank and the media which is ultimately to be placed within a cavity so formed. The purported purpose of the inner banks is to prevent the media from contacting the as yet uncured outer bank by retaining it between the inner banks. This function reportedly prevents the degradation of any electrochemically active compound present in the media. Because of the precision required in measuring the amount of material necessary to form the inner banks and the outer bank, the time required to pre-cure the inner banks and the positioning required with respect to the space interval between the inner banks and the outer bank, the inefficiency of this method is clear. Inasmuch as this method also requires precise measuring of media to fill, but not overflow, the cavity thereby formed, its inefficiency is compounded.
Thus, to date, the available methods for sealing media within the cell cavity of electrochromic devices have proven cumbersome as well as inefficient and often ineffective, and particularly so for devices having large surface area, such as automobile glazings. In view of these shortcomings, it would be desirable to provide a method for sealing such devices that creates the cell cavity at substantially the same time as the media is dispensed. In this way, the sealing material would need not be cured separately prior to dispensing the media and establishing the seal. This method should also allow the media to be dispensed without having to accurately pre-measure it. In addition, such a sealing method should keep the substrates in spaced-apart relationship to one another as a result of the seal itself (not spacer beads having been added thereto) which also keeps the devices themselves intact so that the opportunity for short circuiting is decreased.
Therefore, a definite need exists for a method for sealing electrochromic devices wherein the cell cavity is created at substantially the same time as when the media is dispensed and the seal itself forms, and wherein the media is readily dispensed without requiring precise measurement thereof.